The objective of this investigation is to obtain a differential count in blood smears of lymphocyte subpopulations of normal individuals and patients with malignancies and other diseases by using bacteria as markers. Some bacteria, which do not bind naturally to lymphocytes are chemically coated with antibody against immunoglobulins present on lymphocytes, attached passively, or as heterologous anti-lymphocyte antibody. Other bacteria bind naturally to lymphocytes and identify their subpopulations. For example, Brucella melitensis binds to B cells; other bacteria bind differently to four T and possibly two B cell subpopulations. In principle, the method involves the use of whole blood cells, after the plasma is washed. Bacteria are added in excess, centrifuged for a few minutes to promote the binding. The unbound bacteria are washed out and smears prepared. The subpopulations identified by bacterial adherence have been separated by using bacterial monolayers coupled to gelatin and were found to be functionally different. Studies on normal adult blood samples or cord blood samples and some patients with cancer or leukemia suggest that the percentages of lymphocytes binding bacteria are biological constants which change in disease. For the coming year we propose to investigate patients with malignancies or with autoimmune diseases for the presence in the blood of lymphocytes having two types of light chains. Also, we shall determine whether an abnormal increase in B cells with either kappa or lambda chains can be used as an early indicator of chronic lymphocytic leukemia. We shall also attempt to obtain by mutation and selection, more bacteria capable of identifying normal or activated lymphocytes. The mechanisms of bacterial binding, may be analogous to binding of heterologous erythrocytes to lymphocytes. Our hypothesis is that lectins on the lymphocytes interact with carbohydrates on the bacterial cell wall, and that different subpopulations may have different lectins, probably used in the process of intercellular recognition in the organism. We shall separate and study the molecules involved in binding from bacteria and from the lymphocytes. This investigation may lead to a standard and automated procedure useful in clinical laboratories.